It is well known in the prior art to form copper deposits on plastics and non-conductive materials for providing electromagnetic shield layers thereon. In general, parts which require electromagnetic shield layers to be formed thereon are relatively large in size. Then electroless copper plating techniques are often used for forming copper deposits since uniform deposits can be formed even on such large size parts. More illustratively, copper deposits are formed on plastics and non-conductive materials in accordance with conventional chemical plating techniques by effecting suitable pretreatments such as degreasing and etching, forming metallic palladium or silver nuclei on the surface of non-conductive material for activation and then performing chemical copper plating.
As is well known in the art, better electromagnetic shields are manufactured by paying up an electroless nickel deposit on an electroless copper deposit for protecting the copper deposit against oxidation which would otherwise detract from shielding effect.
In the manufacture of such electromagnetic shields, the electroless copper plating process uses a bath containing a water soluble salt of copper, a complexing agent and a reducing agent, which is typically formalin. However, since the electroless copper plating bath containing formalin as a reducing agent is an alkaline bath due to the inclusion of formalin, it is sometimes difficult to apply to some types of non-conductive material which should be shielded against electromagnetic radiation.
In such cases, an acidic or neutral bath containing hypophosphorous acid or a salt thereof as the reducing agent would be useful. Unfortunately, hypophosphorous acid and salts thereof are relatively expensive chemicals. For electromagnetic shield manufacture which often involves processing of relatively large size parts over relatively large surface areas, an increase in processing cost due to the use of expensive chemicals becomes non-negligible.
Therefore, it is desired to have an electroless copper plating bath of the acidic type capable of forming copper deposits at a cost as low as possible.